How many megapixels is too many?
13th Aug 2008 | 09:49
More is less when quantity comes before quality
Converting all that potential into great pictures depends on much more than just how many pixels can be crammed into an unfeasibly small space.
In 2005, The New York Times reported an astonishing quote from Canon's media director Chuck Westfall: "In compact cameras, I think that the megapixel race is pretty much over," he said. This came at a time when eight megapixels was considered all you could eat in a compact digital camera: enough for a 12 x 7 inches print at 300dpi.
Last week, Samsung announced the NV100HD, whose sensor packs in an incredible 14.7 megapixels. If the race is over, Samsung has sprinted over the hills where it's downing a celebratory Lucozade, while the rest of the field catches its breath.
A 14.7 megapixel camera produces an image 4,384 pixels wide by 3,288 tall. At 300dpi that's enough for a print that measures 14 inches wide by 11 inches high. At 200dpi – still a reasonable resolution to print at – the NV100HD's images weigh in at 22 x 16 inches, or more than half a metre wide.
The sensor in a camera is a modern miracle. A compact camera such as the NV100HD has a sensor that measures approximately 6mm wide by 4.6mm tall: roughly a quarter of the size of a postage stamp. Over 14 million tightly-packed pixels are on that sensor, each with its own tiny lens. Even by the incredible standards of modern technology, that's a breathtaking feat.
This CMOS sensor, taken from a Canon 1000D, packs over ten million pixels into a space just 22.2mm wide by 14.8mm high. So that's it. The more megapixels you have, the better your camera, and the better your pictures will look. That's why megapixels is the biggest number of the specification sheet, right?
Not that simple
Not quite. In fact, it's often the case that the more megapixels on a sensor, the worse the image quality will be. Small sensors already suffer compared to the larger sensors on DSLRs as less light falls on them. The second problem is that to fit 14,000,000 pixels on a sensor, the pixels have to be tiny.
That means they have to be fairly powerful to produce a good, well-exposed image, and that means that there's plenty of voltage flowing across your average sensor.
In turn, this voltage creates noise: electrons get lost and wander about, fooling the pixels into recording the noise as light. The result is the bane of a photographer's life: image noise. And, the higher the ISO your digital camera is set to, the harder your sensor is working, so there's even more noise. Finally, sensors warm up while they're working, and this heat triggers yet more noise, so long exposures are prone to hot pixels.
Big is beautiful
The answer to the problem of image noise is larger sensors. DSLRs have larger sensors than digital compact cameras, and full-frame cameras such as the Nikon D700 and Canon EOS 1D, larger still. Full-frame is so-called because the sensor is almost the same size as a single exposure on a 35mm piece of film.
The logic is easy: if a sensor is four times the size of another, yet they both have the same number of megapixels, the pixels on the large sensor are less densely-packed. Larger sensors require less power to capture the same amount of light, and that means less image noise. The problem, of course, is that large sensors require large camera bodies and high prices: you won't find a full-frame DSLR for under £1,000.
Beauty at a price
The absurdly desirable Nikon D3 has a full-frame, 12.1 megapixel sensor and produces beautiful, low-noise images, but you pay the price: around £3,000 for the body only.
Finally, the sensor is only part of what helps a camera take good pictures. The electronics that process your image and the construction of the lens also play their part.
What more megapixels give you is the ability to crop further into your image: they don't necessarily mean more detail, and they certainly don't mean a better image. After all, it's no good having an enormous image when printing it reveals disruptive, ugly noise.
So will the Samsung NV100HD succeed? We'll only know when review units arrive but until then, Samsung is still running – and winning – the race.